News

Shark tracker pinpoints great white off English coast

OCEARCH photo by R. Snow

This one-ton great white shark named Lydia by the crew of the OCEARCH research vessel was captured and tagged off Florida last March.

By Doug Fraser

Cape Cod Times

(March 11, 2014) The OCEARCH shark-tracking website kept crashing Monday, and Simon Thorrold thought he knew why. It was all the Brits logging in to the website to try to locate the peripatetic great white shark named Lydia, said the senior scientist, and shark researcher, from the Woods Hole Oceanographic Institution.

Quite likely true, since state shark scientist Greg Skomal said he spent a fair amount of his time Monday being interviewed by British journalists. Skomal helped tag the 14-foot, 1-ton female great white in the waters off Florida last winter. Since then, she's been on a nearly 20,000-mile voyage along the East Coast of the U.S., hanging around Newfoundland in January before striking out to cross the big pond.

On Monday, Lydia drew to within less than 800 miles of the English coastline. Although she has been heading north for around a week, if she does reach Great Britain it would be the first documented Atlantic crossing by a white shark, Skomal said.

"I think we were all surprised and have been surprised by Lydia's activity for some time," said Chris Fischer, the expedition leader and founding chairman of OCEARCH, a 126-foot former Alaskan crabber boat that serves as research platform for shark and fish tagging around the world.

OCEARCH staffers maintain the shark tracking website that plots signals from Smart Position and Temperature tags, called SPOT tags, that are bolted onto the great white's dorsal fin after it is caught and raised out of the water on a specially adapted platform on the large vessel. SPOT tags broadcast a locator signal to satellites every time the shark's dorsal fin breaks the surface.

With Lydia in news stories in every major daily in Great Britain, Fischer said, they had to increase the capacity of their Global Shark Tracker website tenfold to accommodate the additional interest from Europe — and the site still crashed.

"It's crazy," Fischer said. He said it showed that people do have a hunger for marine science in general, and sharks in particular.

Skomal has either tagged or assisted in tagging 37 great whites in the four years since his first successful tagging off Chatham in 2009. All but Lydia were tagged in Cape waters, mostly off Chatham, where they prey upon seals in the largest gray seal colony in the U.S.

Most of those sharks were fitted with acoustic tags and archival satellite trackers deployed by harpoon. The acoustic tag broadcasts a unique identifying signal that can be heard by listening devices along shorelines and in boats. The archival tag records environmental information like temperature, depth, light, salinity and location. It downloads that information to a satellite after it detaches itself from the shark and floats to the surface.

When Lydia's satellite tag popped off in June, analysis showed she was diving deep, as far down as 3,000 feet, and surfacing. Scientists believe that may represent deep ocean hunting behavior as the white shark pursues prey in the pitch-­black depths of the sea, where the temperature can range between 37 and 41 degrees, and then surfaces to get warm again, Thorrold said. Some sharks don't surface for months at a time and their SPOT tags can have long gaps between locations, but Lydia has a lot of satellite markings in recent weeks and that is one indication she is likely still diving and surfacing, Thorrold said.

But what is she eating in the middle of the ocean, an area many thought of as a desert, devoid of the amount of prey required to support an apex predator? Thorrold said that thinking is changing. The eastward extension of the Gulf Stream is known as the North Atlantic Drift and the strong current that runs along the East Coast slows and becomes a series of eddies, miles in diameter, drifting eastward, creating little colonies of life held together by the rotational force. Recent papers using acoustic survey techniques have posited that there may actually be abundant dense rafts of life in the middle of the ocean, 600 to 3,300 feet down, shrimp, squid, and other species, feeding off plankton and each other.

But without seeing Lydia diving and then examining her stomach contents, scientists are only guessing, Skomal said.

Tagging studies on other shark species, and tunas, have shown them crossing the Atlantic, but, until now, that hadn't been documented in great whites. Until Mary Lee wandered north in the middle of the winter and hung out off Georges Bank, it was thought that they simple migrated seasonally like birds, north in summer, south for the winter. Lydia adds another layer to what Skomal believes could be a very complex life cycle. Only the SPOT tags, which can last three to five years, have the ability to stay active long enough to reveal some of these patterns.

"That is what is so fascinating," Thorrold said. "Every shark is different."

Skomal said they will have to tag a lot more white sharks, including males who are underrepresented in their current tagging stock, before they can know more of what these patterns mean. For now, he's worried that Lydia may not avoid being caught by fishermen from European countries who don't consider the white shark a protected species, like the U.S., South Africa and Australia do.

Thorrold has a different concern. Now that a fair number of Atlantic great white adult sharks have been tagged, he is worried there are few reports of juveniles. In all other parts of the world where great whites are established, sharks between four and 10 feet long are seen in coastal areas eating fish.

"That leads me to the conclusion that they could be in significant trouble," Thorrold said.